Defining the Hydrate Fugacity and Reference Parameters

Ballard (2002) defined a hydrate fugacity with three major advantages  

The aqueous phase does not need to be present to enable hydrate calculations. Frequently, gas or condensate pipelines have no aqueous phase. 

The properties of the empty hydrate are directly used in the model as opposed to the difference properties suggested by Parrish and Prausnitz (1972). 

The expression for the fugacity of water in the hydrate follows the same framework as that in all other phases (i.e., aqueous, vapor or liquid, or pure solid phases). 

In order to solve for thermodynamic equilibrium, the fugacity of water in the hydrate must be known. This method follows the common approach of solving for fugacity, using the standard state of the ideal gas of the pure component at 1 bar. 

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